The present invention generally relates to projectile velocity measuring apparatus and methods and, more particularly, to electromagnetic wave Doppler muzzle velocity measuring apparatus and methods employing at least part of a weapon barrel as a waveguide.
Yet, more particularly, the invention is directed to projectile velocity measuring apparatus and methods, wherein an electromagnetic wave is coupled to and introduced into the barrel of a weapon via a waveguide connector connected to the muzzle of the barrel and an electromagnetic wave reflected off of a projectile positioned within the barrel is received from the barrel, the phase relationship between the introduced and received waves changing as the position of the projectile changes so as to serve as a measure of the position of the projectile within the barrel.
U.S. Pat. No. 4,283,989, the disclosure of which is incorporated herein, discloses such a method and apparatus. The disclosed apparatus is employed for identifying the speed and acceleration of a projectile situated within a barrel of a weapon while still contained within the barrel. This allows identification of ballistic conditions within the barrel, of ammunition, or for correcting a delayed detonator in a projectile while taking into consideration the actual muzzle velocity of the projectile.
Generally, the apparatus and method employs electromagnetic waves in the microwave region (wavelengths in millimeters or centimeters), the wavelength employed depending on the caliber of the barrel of the weapon under evaluation. The barrel is employed as a waveguide for microwaves coupled thereto for introduction into the barrel. Different wave types or modes form in the waveguide depending on the frequency employed and the caliber of the barrel. In order to guarantee unambiguous measurements, the frequency of the microwave and the nature of the coupling of the microwaves to the barrel are selected so that only one wave type develops.
The projectile positioned within the barrel of the weapon acts as a sliding short circuiting component at which the introduced wave reflects so that a standing wave is formed within the barrel as a result of the superimposition of the introduced and reflected waves. When the projectile is fired, the projectile, in a sense, causes the standing wave to travel along the barrel in front of the projectile as the phase relationship between the introduced and reflected wave shifts or changes.
The phase shift produced by the motion of a fired projectile can be detected and identified by a suitable evaluation arrangement that measures Doppler frequencies. The apparatus outlay or hardware corresponds substantially to that of a low-power Doppler radar. However, there are a variety of adaptations necessary for coupling the wave to be introduced into the barrel to the barrel and to receive the reflected wave.
Early Doppler radar apparatus employed for determining projectile velocities used antennas, deflecting mirrors, and the like for introducing the waves into and receiving the waves out from the barrel. These components were always at least partially destroyed by a projectile emerging from the barrel upon firing. Accordingly, these are referred to as apparatus for destructive identification of ballistic characteristics within a barrel of a weapon. More recent apparatus, such as that disclosed in U.S. Pat. No. 4,283,989, employ components that are not destroyed by a fired projectile and, accordingly, are referred to herein as apparatus for nondestructive identification of ballistic characteristics within a barrel of a weapon.
There is no known system or apparatus in the marketplace that is usable in practice. With the known systems and apparatus, the mechanical stresses of the barrel that arise from firing of the projectile immensely influence the evaluation of the ballistic characteristics because the mechanical stresses create signals that are relatively high, while the levels of signals employed during the evaluation are relatively low.
Although signals that can be easily evaluated can be generated by the apparatus of the prior art, the useful or measurement signal substantially degrades upon a line firing. This occurs because the useful signal is overridden by disturbance signals having the same order of magnitude as the useful signal. Other reasons are noted in the disclosure of U.S. Pat. No. 4,283,989.